1. Field of the Invention
The present invention relates to an electroconductive paste and a method for manufacturing multilayer ceramic electronic parts using the paste. More particularly, the present invention relates to an electroconductive paste suitable for forming a via hole conductor and a method for manufacturing multilayer ceramic electronic parts using the paste.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 11-329895 is a prior art reference which is interesting for the present invention. It discloses a method for manufacturing multilayer ceramic electronic parts. It teaches basically a method in which a group of electronic parts is formed, and it is then cut along specific division lines to establish a plurality of multilayer ceramic electronic parts.
More specifically, multilayer ceramic electronic parts are provided by the steps of: forming a raw laminate by laminating ceramic green sheets with via hole conductors formed therein which are to be converted to external electrode terminals, and ceramic green sheets with no such via hole conductors formed therein; forming grooves on the raw laminate so as to bisect the via hole conductors; exposing parts of the via hole conductors on the inside surfaces of the grooves; next, firing this raw laminate for sintering; and then, dividing the laminate after sintering along the grooves so as to realize multilayer ceramic electronic parts, wherein the parts of the via hole conductors are converted to the external electrode terminals.
According to this conventional technology, the external electrode terminals can be easily formed even if the allocation pitch is small. It is also possible to perform measurement of properties of individual multilayer ceramic electronic parts on a laminate at the stage after sintering and before the group of electronic parts is divided along the grooves.
On the other hand, Japanese Unexamined Patent Application Publication No. 10-172345 discloses an electroconductive paste which can be advantageously used for forming via hole conductors. It teaches that this electroconductive paste contains a resin powder composed of a resin such as a crystalline cellulose that is insoluble in a solvent contained in the paste, and accordingly, cracks in the via hole conductors or breaking of the peripheral ceramic areas are prevented from occurring at the time of firing, and therefore, via hole conductors can be formed, which have a high reliability of electroconductance and an excellent solderability as well as an excellent plating capability.
However, even if the electroconductive paste disclosed in Japanese Unexamined Patent Application Publication No. 10-172345 is used as the electroconductive paste for forming via hole conductors in the method for manufacturing multilayer ceramic electronic parts disclosed in Japanese Unexamined Patent Application Publication No. 11-329895, there would be a problem in that the via hole conductors are deformed due to their volume expansion caused by water absorption of the resin powder existing in the electroconductive paste for forming the via hole conductors when a dicing saw is employed in performing the step of forming grooves on a raw laminate for bisecting the via hole conductors, so that parts of the via hole conductors are exposed to be converted to external electrode terminals. This is because water is usually sprayed when a dicing saw is employed.
Accordingly, it is an object of the present invention to provide an electroconductive paste that can solve such a problem and to provide a method for manufacturing multilayer ceramic electronic parts using the paste.
The present invention is first directed to an electroconductive paste used for forming a via hole conductor in a method for manufacturing a multilayer ceramic electronic part comprising the steps of: manufacturing a raw laminate composed of a plurality of laminated ceramic green sheets including ceramic green sheets with the via hole conductor therein; and cutting the raw laminate at an area where the via hole conductor is located, and exposing part of the via hole conductor on the cut surface, so that the via hole conductor is converted to an external electrode terminal. To solve the above-described technical problems, the electroconductive paste comprises: from about 5% to 18% by weight of an organic vehicle comprising a solvent and a binder; from about 80% to 93% by weight of an electroconductive metal powder in a spherical or granular shape and with a particle diameter in the range of about 0.1 to 50 xcexcm; and from about 2% to 10% by weight of a resin powder with a particle diameter in the range of about 0.1 to 50 xcexcm that is insoluble in the above-described solvent and has a low level of water absorption.
As the above-described electroconductive metal powder, a copper powder can be used, for example.
It is also preferable that the resin powder is a polypropylene powder.
Another aspect of the electroconductive paste according to the present invention is characterized in that it contains an electroconductive metal powder, an organic vehicle, and from about 2% to 10% by weight of a polypropylene powder. The electroconductive paste according to the present invention can be used not only for forming the above-described via hole conductors but also for other applications.
In the above-described aspect of the present invention, the electroconductive paste preferably comprises from about 80% to 93% by weight of the electroconductive metal powder, and from about 5% to 18% by weight of the organic vehicle.
The present invention is also directed to a method for manufacturing a multilayer ceramic electronic part comprising the steps of: manufacturing a raw laminate composed of a plurality of laminated ceramic green sheets including ceramic green sheets with a via hole conductor therein; cutting the raw laminate at an area where the via hole conductor is located, and exposing part of the via hole conductor on the cut surface, so that the via hole conductor is converted to an external electrode terminal; and firing the raw laminate having the via hole conductor partly exposed on the cut surface for sintering. This manufacturing method is characterized in that the above-described electroconductive paste is used as an electroconductive paste for forming the via hole conductor.
Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.